Semiconductor integrated circuits of a specific desired type are normally formed through a semiconductor device manufacturing process during which various types of processing such as film formation processing, etching, heat processing, refining and crystallization processing are executed repeatedly on a processing target substrate, e.g., a semiconductor wafer (hereafter may simply be referred to as a “wafer”) or a glass substrate. Such processing is executed by delivering a specific processing gas corresponding to the particular type of processing being executed into a processing chamber.
For instance, a plane-parallel plasma processing apparatus equipped with an upper electrode and a lower electrode disposed inside a processing chamber as disclosed in Japanese Laid Open Patent Publication No. 2003-257937 is normally used in an etching process. The lower electrode also functions as a stage on which the processing target substrate is placed, with its upper surface formed so that it supports the processing target substrate levelly. The upper electrode, which also functions as a gas supply device utilized to deliver the processing gas into the processing chamber, is disposed above the lower electrode so as to face opposite the lower electrode.
A gas supply pipe is connected to the upper electrode and a processing gas supplied through the gas supply pipe travels inside the upper electrode and is then injected toward the processing target substrate placed on the lower electrode through numerous gas injection holes formed at the lower surface of the upper electrode. As high-frequency power is applied to the upper electrode and the lower electrode during this process, the processing gas supplied into the space above the processing target substrate is raised to plasma. The plasma thus generated is used to etch a film formed on the processing target substrate or to form a specific type of film over the processing target substrate.
A structural example adopted in an upper electrode in the related art, which includes a processing gas supply mechanism such as that described above, is now explained in reference to a drawing. FIG. 7 schematically illustrates the structure of the upper electrode in a sectional view. The upper electrode 10 in FIG. 7 is constituted with a processing gas supply mechanism main unit 12 and a plate-type electrode 16 layered over the lower surface of the processing gas supply mechanism main unit 12.
An electrode rod 18 via which a high-frequency voltage originating from a high-frequency power source (not shown) is supplied to the upper electrode 10 is disposed near the center at the top of the processing gas supply mechanism main unit 12. In addition, a gas supply pipe 20 through which the processing gas is supplied to the upper electrode 10 is connected via a processing gas delivery port 22 at the top of the processing gas supply mechanism main unit 12.
Inside the processing gas supply mechanism main unit 12, a diffusion chamber 24 through which the processing gas delivered from the gas supply pipe 20 via the processing gas delivery port 22 is diffused along the horizontal direction is formed. A plurality of processing gas supply holes 25, which range from the diffusion chamber 24 through the lower surface of the electrode plate 16 are formed so as to pass through the processing gas supply mechanism main unit 12 and the electrode plate 16.
At the upper electrode 10 structured as described above, the processing gas delivered into the diffusion chamber 24 via the processing gas delivery port 22 is diffused and distributed toward the individual processing gas supply holes 25. The processing gas then travels through the various processing gas supply holes 25 and is let out downward.
As plasma is generated in the processing chamber of a plasma processing apparatus equipped with the upper electrode 10, the temperature of the upper electrode 10 rises due to the heat input from the plasma. In addition, as the stage is heated during the plasma processing, for instance, the heat radiated from the stage raises the temperature of the upper electrode 10 as well. Such an increase in the temperature of the upper electrode causes thermal expansion of both the processing gas supply mechanism main unit 12 and the electrode plate 16 constituting the upper electrode 10.
Since the processing gas supply mechanism main unit 12 and the electrode plate 16 are normally constituted of materials with different coefficients of thermal expansion, the processing gas supply mechanism main unit 12 and the electrode plate 16 thermally expand to different extents. For instance, if the processing gas supply mechanism main unit 12 is constituted of aluminum and the electrode plate 16 is constituted of quartz, the processing gas supply mechanism main unit 12 will thermally expand to a greater extent along the lateral direction than the electrode plate 16, since the coefficient of thermal expansion of aluminum is greater than the coefficient of thermal expansion of quartz.
However, if the upper electrode 10 is surrounded by a shield ring (not shown) or the like disposed along the edge thereof, the thermal expansion of the processing gas supply mechanism main unit 12 along the horizontal direction is restricted by the shield ring or the like, causing the processing gas supply mechanism main unit to start warping slightly ahead of the electrode plate 16, as the process of thermal expansion progresses. Such a slight extent of warping creates a small gap at the boundary of the processing gas supply mechanism main unit 12 and the electrode plate 16. Under such circumstances, some of the processing gas flowing through the processing gas supply holes 25 will leak through the gap 25, as shown in FIG. 8.
The processing gas leak through the gap formed at the boundary of the processing gas supply mechanism main unit 12 and the electrode plate 16 occurring due to the thermal expansion and the like as described above will reduce the flow rate of the processing gas let out through the processing gas supply holes 25. In such a case, since the processing gas is not let out through the processing gas supply holes 25 at the expected flow rate, the target area on the wafer, which should be processed with the processing gas supplied through the processing gas supply holes 25 at the expected flow rate, can no longer be processed at the desired film formation rate or etching rate and thus, the desired processing results may not be achieved.
In addition, the processing gas leaking from a processing gas supply hole 25 may travel through the gap 26 at the boundary of the processing gas supply mechanism main unit 12 and the electrode plate 16 to flow into another processing gas supply hole 25, e.g., an adjacent processing gas supply hole 25. As a result, the processing gas may be let out through the various processing gas supply holes 25 at different flow rates. Furthermore, since numerous processing gas supply holes 25 are formed over the entire surface of the electrode plate 16, the temperature distribution at a given processing gas supply hole is bound to be different from the temperature distribution at another processing gas supply hole. This means that the thermal expansion will occur to varying extents, which, in turn, results in the processing gas leaked through the individual processing gas supply holes in different quantities. In other words, the processing gas may not be let out through the various processing gas supply holes 25 at the uniform flow rate. If such inconsistency is significant, the required level of processing uniformity may not be achieved within the plane of the wafer W.